(1) Field of the Invention
The present invention relates to the field of systems for evaluating the behavior of a moving mechanical part in the context of an application to rotors on rotorcraft. The present invention relates more particularly to systems for monitoring the moving behavior of a blade of such a rotor in flapping and/or in lag (i.e. in the lead-lag direction).
(2) Description of Related Art
The present invention provides a rotorcraft rotor fitted with an appliance for capturing information relating to the moving behavior of a blade of the rotor. Said capture appliance is organized to enable the tilting behavior of the blade to be monitored, and more particularly its behavior in flapping and/or in lag, relative to a rotary hub that drives the rotor in rotation.
Rotorcraft are aircraft provided with at least one rotor for driving a rotary wing in rotation. The rotor is constituted in particular by a main rotor that provides at least lift and usually also propulsion for the rotorcraft, or it is a tail rotor that serves to guide the rotorcraft in yaw. The rotor may also be a propulsion propeller, e.g. as used in particular for fitting to a hybrid helicopter.
The rotary wing has blades that are mounted via respective blade roots on a rotor hub that is driven in rotation by a power plant. There are two or more blades, and the blades are radially distributed around the hub. The blades are hinged to the hub and can be operated by a pilot to pivot about their own axes in order to modify the flight behavior of the rotorcraft. Modification of the flight behavior of the rotorcraft is achieved by varying the pitch of the blades at least collectively, and usually also cyclically. The pilot may be constituted in particular either by a person and/or by an autopilot operating under the control of that person.
More particularly, a pilot can cause rotor blades to pivot about their own axes so as to vary their pitch about an axis extending in the general direction in which they extend. Blades are also movable in tilting in their general plane, in flapping and in lag. Such tilting movements of the blade are caused in particular under the effects of the blade being driven in rotation and of aerodynamic effects induced by the blade. The angles of tilt of the blade in flapping and in lag correspond respectively to an angle of tilt of the blade that is transverse or radial relative to the axis of rotation of the hub.
There arises the problem of monitoring the moving behavior of the blade in flapping and/or lag relative to the hub. The present invention seeks to monitor the moving behavior of the blade and to collect pertinent information about the movements to which it is subjected, in particular in flapping and/or in lag. It is more particularly desired to obtain a reliable and accurate analysis of the movements to which the blade is subjected.
Such monitoring is desired in order to assess the lifetime of the mechanical parts making up the rotor, and in order to better organize maintenance operations on the rotor. On the basis of such monitoring, maintenance operations may be performed in response to real needs as determined with respect to the movements that have actually been performed by the blades in flapping and/or in lag.
Such monitoring may also be advantageous for increasing rotorcraft safety. For example, on the basis of monitoring the behavior of the blades, it is possible in real time to alert an operator, and in particular the pilot of the rotorcraft, about a potential failure or about the rotor working excessively or inadequately.
Such monitoring is also desirable to identify potential improvements that could be made to the rotor, concerning its structure and/or its operation, by examining the movements to which the blades are actually subjected over a period and/or during given flying missions.
The behavior of a blade in pivoting so as to vary its pitch is readily determined from the flight controls operated by the pilot. In order to assess all of the movements to which the blade is subjected, there arises the particular problem of monitoring the tilting behavior of the blade, more particularly in flapping and/or in lag. Specific solutions should be implemented in order to monitor the flapping and/or lag movements of the blade.
A system for monitoring the flapping and/or lag behavior of a mounting assembly for mounting blades on the hub of a rotor is known from document FR 2 774 655 (Eurocopter Deutschland). The intention is to detect critical loading states and risks of incidents on the rotor, by detecting torques applied to the hub by all of the blades in flapping and/or in lag.
Said mounting assembly is made up of a plate secured to the blade roots carrying respective blades. The plate forms a common junction member for joining the blade roots to the hub of the rotor. The mounting assembly is made flexible in flapping and/or in lag by the structural arrangement of the blade roots and the plate. The monitoring system comprises strain gauges installed on the mounting assembly in the junction zones between the blade roots and the plate. The strain gauges generate information derived from the deformations to which the mounting assembly is subjected in its general plane and caused by the effects of flapping and/or lag movements of the blades.
The monitoring system proposed in FR 2 774 655 is simple in structure, but it provides limited information about the effects induced on the rotor by the flapping and/or lag movement of the blades. Such information suffices in particular for activating actuators that modify the behavior of the mounting assembly in flapping. In addition, the application of such a monitoring system is restricted to the type of rotor that makes use of a said mounting assembly.
The monitoring system as described in FR 2 774 655 needs to be improved, in order to optimize potential analysis of the movements of the blades in flapping and/or in lag, and in order to increase the uses that can be made of such optimized analysis. The monitoring system also needs to be improved to make it potentially applicable to a rotor that is arranged in any manner, in particular concerning the ways in which the blades are joined to the hub.
Reference may also be made to document US 2010/101335 (Volanthen M. et al.), which describes a system making use of optical sensors for measuring the stresses to which the blades of a rotorcraft rotor are subjected.
Reference may also be made to document US 2008/036617 (Arms Steven W. et al.), which discloses a system for monitoring the behavior of a component of a rotorcraft rotor. A sensor associated with memory means detects the forces to which the component is subjected in order to replace a component that has been subjected to excessive forces.
Reference may also be made to document DE 10 2006 037900 (EADS Deutschland), which discloses a system for monitoring the tensions to which a rotor blade of a rotorcraft are subjected, by making use of a strain gauge implanted at the end of the blade.
Another difficulty to be overcome is associated with the rotating nature of the rotary wing, which makes it difficult to use strain gauges installed on the rotary wing. The rotary nature of the rotary wing also makes it difficult to deliver the electrical power needed to make the monitoring system operate, nor the transfer information from the rotary wing to a member for collecting the information.
In order to illustrate such a difficulty, mention is made by way of example in document US 2010/216398 (Sikorsky Aircraft Corp.) of using transducers in the context of an application to a rotorcraft rotor. More particularly, a solution is proposed for avoiding signal interference between the transmitter and the receiver that are respectively located on a rotor and on a main gearbox of a power plant of the rotorcraft.
Transducers include surface acoustic wave (SAW) transducers. The operation of SAW transducers is based on the principle of the inverse piezoelectric effect. A transducer is placed on a piezoelectric surface and is installed on a mechanical part that is to be monitored. The SAW transducer receives an electromagnetic wave from an interrogation unit, which wave is converted into an acoustic wave. Modification to the physical properties of the acoustic wave is indicative of a modification in the behavior of the mechanical part on which the transducer is installed. The modified acoustic wave is converted in an electromagnetic wave by the SAW transducer and is transmitted to the interrogation unit at given frequencies.
SAW transducers present the advantage of being passive, with the energy needed for making the transducer operate being provided by the electromagnetic wave that is transmitted by the interrogation unit. The information delivered by SAW transducers to the interrogation unit is of good quality, being pertinent and reliable for separation distances between a SAW transducer and the interrogation unit that may be of the order of several meters. SAW transducers can be used as strain gauges, as disclosed in document U.S. Pat. No. 6,810,750 (Invocon Inc.).
In the field of monitoring the operation of a mechanical member, health and usage monitoring systems (HUMS) are also known. By way of example, HUMS systems can be used to monitor temperature in a moving environment and/or to monitor the operation of a moving assembly relative to a stationary structure. The movement of the moving assembly is evaluated by a HUMS system in order to detect any possible defects in its dynamic behavior. HUMS systems are used in the field of rotorcraft.
HUMS systems make use of transducers that associate an information transmitter and a receiver of the transmitted information. The receiver and the transmitter are suitable for being installed respectively at a distance apart from each other, one on a stationary structure and the other on a structure that is movable relative to the stationary structure. Information is transmitted between the transmitter and the receiver by means of waves in order to avoid using a wired connection, which is made difficult because of the relative movement between the stationary structure and the movable structure that is to be monitored.
The accuracy, the pertinence, and the reliability of the information delivered by information sensors, in particular by transducers, depend closely not only on their own specific capacities, but also on features relating to how they are installed on a member that is to be monitored. Such installation features need to be appropriate for enabling good use to be made of the intrinsic performance of the information sensors used. For a rotorcraft rotor, the performance desired for the information sensors must not require them to occupy a large amount of the junction zone between the blade and the hub in order to be installed. The environment of said junction zone must in particular remain available for installing other members, such as pitch rods for pivoting the blades and/or other operating members commonly to be found in rotorcraft rotors.
The ways in which a blade root and a hub are joined together can be complex. For example, the blade root is potentially mounted to be removable from the hub via abutment members such as rolling bearings or a spherical abutment, for example. It is desirable for the ways in which information sensors are installed to be suitable for a rotor of any kind, and more particularly regardless of the ways in which blade roots are joined to the hub.
The use of high performance transducers is appropriate for evaluating the behavior of a blade in flapping and/or in lag. This gives rise to the specific problem of how they are to be installed on the rotor while being able to perform this function, in particular concerning the above-mentioned constraints and difficulties.
A compromise needs to be found in particular between simple, appropriate, and pertinent techniques for performing such an installation, and making best use of the capacities and of the performance of the transducers used. Such a compromise must also take account of ease of installation of the transducer(s) on the rotor, it must be transposable to any kind of rotor without significantly affecting its weight and/or its balance, and more particularly it must be transposable regardless of the way in which blade roots are joined to the hub.